'brave' is rumoured to have many origins. Some say it originates of the words 'bastard' and 'rave' whilst others believe in a a more complicated constellation consisting the words 'bastard', 'radical' and 'safe'. Either way the common use and interpretation of the two meanings does not differ too much in everyday life. It is an expression to highlight someone's high social value in community adding this extra bit of hidden meaning for people familiar with this expression. It can be used as an adjective or an adverb. In some cases it might even be used as a noun.

-'Brave, mate?'
-'Sure bro, braver...'

-'Mick banged that super hot chick last week and than `snorted 4 grams of cocaine'
-'Brave!'